Apparatus for making dental castings are well known and have been in use for many years. For example, a Emerick U.S. Pat. No. 4,150,707 discloses a method and apparatus for making dental castings. As disclosed, a method and apparatus for making dental castings wherein a crucible is supported on a platform having a central opening positioned beneath the crucible over a mold cavity of the investment, This in turn is supported on a platform having a central opening. The upper platform is lowered against the investment so that a single sealed vessel comprising the crucible and investment cavity is formed. Air is then administered to the crucible and investment cavity at a point beneath the crucible opening so that both the investment and crucible may be purged. An arc is formed in the crucible thereby melting the casting material, and air under pressure is admitted to the top of the crucible thereby causing the molten casting material to flow into the investment cavity.
An additional U.S. Pat. No. 4,497,658 of Woog discloses a compact precious metal furnace and recovery method. The Woog patent discloses a highly compact and efficient tilting crucible furnace and smelting method for use in the direct smelting of a precious metal containing material. A furnace body having a refactory lined cavity which has a top opening is pivotally mounted on a support frame to allow tipping thereof. A cover having a first opening to receive a gas burner and a second multi-purpose opening therein is rigidly attached to the body. A gas burner attached to the cover provides a downwardly directed oxidizing flame into the cavity to oxidize iron which is added to the cavity and other impurities in the precious metal containing material. A flux is provided to a thoroughly liquid mixture and after heating the molten mass is poured through the multi-purpose cover opening into a mold. As the mold cools, a doré button of precious metal settles to the bottom of the mold and slag containing impurities forms on the top.
A further Santilli U.S. Pat. No. 4,628,895 discloses a kiln and autonomous heat source portable integrated unit. As disclosed therein, the invention belongs to the technical field for equipment destined for hobby use and, in particular, relates to a portable kiln and heat source integrated unit. The disclosure envisages there being a combination of a portable kiln with a firemouth positioned at the bottom of the kiln; a support structure able to set the kiln in a removeable fit-lock way on a burner facing the firemouth and heat insulating means of protection designed to safeguard at least the elements placed adjacent to the firemouth.
Finally a more recent U.S. Patent of Hohenshelt et al., U.S. Pat. No. 7,458,809 discloses a portable kiln having a set of wheels, a handle and a platform base. The wheels and the handle are attached on a first side of the kiln so that the kiln can be tilted and rolled on the wheels using the handle. The platform base provides a spaced distance between the wheels and the floor when the kiln is sitting upright in an operational position. The kiln may also include a metal outer shell wrapped about an oven portion. The outer shell has a shell sidewall radially spaced from the oven portion sidewall which forms an annular air channel between the outer shell sidewall and the oven portion. The outer shell has a C-shaped cross-section and it has upper and lower vent openings for the air channel. A hinge assembly allows a lid of the kiln to rest in an open position.
Notwithstanding the above, it is presently believed that there is a need and a potential commercial market for an improved thermal oven in accordance with the present invention. There should be a need for such ovens because they are of simple design, rugged, portable and can be constructed at a reasonable cost. Such ovens are suitable for use by hobbyist or dentist to smelt relatively small amounts of gold or precious metals.